Wedge-bonding of wires in electronic device manufacture with reversible wedge bonding tool

ABSTRACT

In the manufacture of electronic devices ( 22, 22 ′), e.g. discrete semiconductor power devices or ICs, a reversible bonding tool ( 10 ) is used having a bonding tip or wedge ( 1, 2 ) at each of its opposite ends ( 11, 12 ). After extensive use of the wedge-tip ( 1 ) at one end ( 11 ) for bonding wires ( 21 ), the tip ( 1 ) is worn somewhat. Instead of needing to replace the bond tool as in the prior art, the tool ( 10 ) in accordance with the invention is then reversed to use the wedge-tip ( 2 ) at the opposite end ( 12 ) for bonding further wires ( 20 ′). Thus, a cost saving is achieved with regard to tool material.

This invention relates to the wedge-bonding of wires in the manufactureof electronic devices. In particular, it relates to wedge-bondingmethods, machines and tools, and also to electronic devices that includeconnections in the form of wires which are wedge-bonded using suchmethods or machines or tools.

The wedge-bonding of wires is a well-established technology that hasbeen used for many decades to provide connections in electronic devices.By way of example, the following is a selection of recent United Statespatents on wedge bonding: U.S. Pat. No. 6,354,479, U.S. Pat. No.6,135,341, U.S. Pat. No. 5,958,270, U.S. Pat. No. 5,950,903, U.S. Pat.No. 5,945,065, U.S. Pat. No. 5,906,706, U.S. Pat. No. 5,836,071, U.S.Pat. No. 5,702,049, U.S. Pat. No. 5,495,976, U.S. Pat. No. 5,452,838,U.S. Pat. No. 5,445,306, U.S. Pat. No. 5,364,004, U.S. Pat. No.5,217,154, U.S. Pat. No. 5,148,959, U.S. Pat. No. 5,018,658, and U.S.Pat. No. 5,007,576. The whole contents of these U.S. patents are herebyincorporated herein as reference material. The bonding tool (typicallyof tungsten carbide) generally comprises a shank having thewedge-bonding tip at one end.

There is always a desire for cost reduction. One of the many items thatinvolves an on-going cost is the need to periodically replace the bondtool when its bonding tip is becoming worn through use.

It is an aim of the present invention to reduce the cost of replacingthe bond tool.

According to one aspect of the invention, there is provided a reversiblebonding tool having a wedge-bonding tip at opposite ends of the tool.Thus, the present invention provides a dual-tip reversible tool, thatincreases the use time before replacement of the tool is required. Thus,a saving can be achieved in tool material.

According to another aspect of the invention, there are providedwire-bonding machines having such a reversible bonding tool inaccordance with the present invention.

According to a further aspect of the invention, there are providedwedge-bonding methods, wherein:

-   -   a reversible bonding tool in accordance with the present        invention is used,    -   and, after using the tip at one end for bonding wires, the tool        is reversed to use the wedge-bonding tip at the opposite end for        bonding further wires.

According to yet another aspect of the invention, there are providedelectronic devices, for example an integrated circuit or a powersemiconductor device, that include connections in the form of wireswhich are wedge-bonded using such a method or machine or tool inaccordance with the present invention.

Various advantageous features and feature-combinations in accordancewith the present invention are set out in the appended Claims. These andothers are illustrated in embodiments of the invention that are nowdescribed, by way of example, with reference to the accompanyingdiagrammatic drawings, in which:

FIGS. 1A and 1B are a schematic side-view of part of an ultrasonicwedge-bonding machine in an embodiment of the present invention, duringuse at successive times in the manufacture of electronic devices;

FIG. 2A is a downward-looking perspective view of the reversible bondingtool of FIG. 1, particularly of its working ends, and showing a bondingtip at its upper end in accordance with the invention; and

FIG. 2B is a upward-looking perspective view of the lower working end ofthe bonding tool of FIG. 2, showing the bonding tip at this lower end.

It should be noted that all the Figures are diagrammatic. Relativedimensions and proportions of parts of these Figures have been shownexaggerated or reduced in size, for the sake of clarity and conveniencein the drawings. The same reference signs are generally used to refer tocorresponding or similar features in modified and different embodiments.

FIGS. 1A and 1B illustrate a wire-bonding stage in the manufacture ofelectronic devices 20, 20′, for example discrete semiconductor powerdevices or semiconductor integrated circuits (ICs). A reversibledual-tip bonding tool 10 is used having a bonding tip (also termed“wedge”) 1, 2 at each of the opposite ends 11, 12 of the tool, see FIGS.2A and 2B.

After extensive use of the wedge-bonding tip 1 at one end 11 for bondingwires 21 (as illustrated in FIG. 1A), the tip 1 is worn somewhat.Instead of needing to replace the bond tool as in the prior art, thetool 10 in accordance with the present invention is then reversed to usethe wedge-bonding tip 2 at the opposite end 12 for bonding further wires21′ (as illustrated in FIG. 1B). Thus, a cost saving is achieved withregard to tool material.

Apart from using the reversible tool 10 in accordance with the presentinvention, the wedge-bonding process and the wire-bonding machine may beof known forms and so will not be described in detail.

Thus, FIGS. 1A and 1B illustrate the work area of the machine, where thedevice 20, 20′ is placed on a work mount 32. Wire 21, 21′ is fedcontinually into this work area from a spool (not shown). The wire 21,21′ is fed to a bond pad 23, 23′ of the device 20, 20′, and it ispressed against the bond pad 23, 23′ by the lower working end (11 inFIG. 1A; 12 in FIG. 1B) of the tool 10. The wire 21, 21′ may comprisealuminium (typically an Al alloy) for both discrete power devices andfor ICs, and the bond pad 23, 23′ may also comprise aluminium. In somedevices, it may be preferred to use gold wire 21, 21′. The wire 21, 21′forms electrical connections between, for example, the bond pad 23, 23′and terminal leads of the device package (not shown).

While being pressed against the bond pad 23, 23′, the wire 21, 21′ isbonded to the pad 23, 23′ by turning on an ultrasonic source to atransducer 30 that applies ultrasonic energy to the wire 21, 21′ on thepad 23, 23′ via the respective bonding tip 1 or 2 of the tool 10. FIGS.1A and 1B schematically show the tool 10 mounted in a horn of thetransducer 30. The horn can be of known form coupled to the source (notshown) of the ultrasonic energy.

In the embodiment illustrated in FIGS. 1A and 1B, the bond tool 10comprises a shank, with tapered work ends 11 and 12 at the opposite endsof the shank. Narrow bonding tips 1 and 2 (which engage with the wire21, 21′ to be bonded) are present at these work ends, specificembodiments being shown in FIGS. 2A and 2B. In the interests ofsimplicity of drawing, the taper is not shown in FIGS. 2A and 2B.

There are a variety of known geometries and structures that may beadopted for the work end and wedge tip. FIGS. 1A, 1B, 2A and 2Billustrate a very simple grooved structure for the tips 1, 2 at theopposite working ends 11, 12, formed integral with the shank. In thiscase, the entire bonding tool 10 (its shank, its ends and its tips) maybe of tungsten carbide. The single groove illustrated for each tip 1 and2 in FIGS. 2A and 2B serves for retaining the wire in position againstthe bond pad during the ultrasonic bonding. In more complex tip designs,cross-grooves and/or protrusions may also be included.

FIGS. 1A and 1B do not show any detail of the wire-bonding machine inrespect of the mounting of the tool 10 in the transducer horn 30. Thismount 31 couples the tool 10 ultrasonically to the transducer in knownmanner. However, the form of the mount 31 and the tool shank are such asto allow the tool 10 to be reversed in the mount 31, so as to permitwire bonding using either the wedge-bonding tip 1 at one end 11 (FIG.1A) or the wedge-bonding tip 2 at the opposite end 12 (FIG. 1B).

This reversible mount aspect is most readily achievable when the mount31 engages the shank of the tool 10 at a position in between itsopposite ends 11, 12. In the embodiment illustrated in FIGS. 1A and 1B,there is a different mount position on the tool shank when therespective ends 11 and 12 are used, but the shank is of the same (i.e.uniform) cross-section along at least the length(s) where these mountpositions are present.

The drawings have shown only a very simple basic form for the tool and aschematic representation of the machine and of the bonding process. Itwill be apparent to persons skilled in the art that this basic form canbe extended, embellished and modified with the type of features that arecommonly used or sometimes used in the art.

Thus, for example, FIG. 1 does not show how the wire 21, 21′ may beguided and fed to the device bond pad 23, 23′. A guide that is externalto the bond tool 10 may be used close to the working tip 1, 2 when thetool 10 has the very simple structure illustrated in FIGS. 1 and 2. Inother embodiments, a guide hole for the wire may be present in the bondtool 10. Thus, for example, separate guide holes (providing a throughpassage for the wire 21, 21′) may extend obliquely through each end 11,12 of the tool 10, or there may be a single feed hole (in the form of acapillary bore) that extends through the length of the tool 10.

In the embodiment described above, the whole bond tool 10 is composed oftungsten carbide. However, other embodiments may use other materials,for example, using hardened steel for the shank or titanium carbide forthe shank.

Different known materials may be used for different parts of the tool 10(the shank, the work ends 11 and 12, and the bonding tips 1 and 2), bothbulk materials and coatings. The shank itself may be formed of arelatively hard, stiff material having a high modulus of elasticity(such as tungsten carbide, hardened steel, or titanium carbide), whereasother materials that are hard, precision-shaped and more abrasionresistant may be used at its opposite ends 11 and 12. Thus, for example,the bonding tips 1 and 2 themselves may comprise a ceramic material oranother, more expensive material such as diamond or osmium.

From reading the present disclosure, many other variations andmodifications will be apparent to persons skilled in the art. Suchvariations and modifications may involve equivalent and other featureswhich are already known in the design, manufacture and use ofwedge-bonding tools and machines and of electronic devices havingwedge-bonded wires, and which may be used instead of or in addition tofeatures already described herein. Examples of such features are to befound in the US patents cited herein previously as reference material.

Although Claims have been formulated in this Application to particularcombinations of features, it should be understood that the scope of thedisclosure of the present invention also includes any novel feature orany novel combination of features disclosed herein either explicitly orimplicitly or any generalisation thereof, whether or not it relates tothe same invention as presently claimed in any Claim and whether or notit mitigates any or all of the same technical problems as does thepresent invention.

The Applicants hereby give notice that new Claims may be formulated tosuch features and/or combinations of such features during theprosecution of the present Application or of any further Applicationderived therefrom.

1. A method of wedge-bonding wires in the manufacture of electronicdevices, wherein: a reversible bonding tool is used having a mount thatengages an elongated shank in a first position between opposite ends ofthe shank, each end including a wedge-bonding tip, and, after using thewedge-bonding tip at one end for bonding wires, the shank is reversedand engaged by the mount in second position between opposite ends of theshank to use the wedge-bonding tip at the opposite end for bondingfurther wires.
 2. A method according to claim 1, wherein the shank ismade of tungsten carbide.
 3. A method according to claim 1, wherein thewires comprise aluminum or gold and are ultra-sonically bonded using atransducer coupled to the tool.
 4. A method according to claim 1,wherein the shank has the same cross-section at the first and secondpositions.
 5. A method according to claim 1, wherein the shank includesone or more guide holes for feeding the wires to the wedge-bonding tips.6. A method according to claim 5, wherein the one or more guide holesincludes separate guide holes extending obliquely through each end ofthe shank.
 7. A method according to claim 5, wherein the one or moreguide holes includes a capillary bore that extends from end to endthrough the length of the shank.